Cannot send RedisFuture between thread

[boxdot]

This minimal example tries to execute a Redis command on a thread-pool (using the latest master)

extern crate redis;
extern crate futures;
extern crate tokio_threadpool;

use futures::Future;
use redis::Client;
use tokio_threadpool::ThreadPool;

fn main() {
    let client = Client::open("redis://localhost").unwrap();

    let work = client.get_async_connection().and_then(|conn| {
        let mut cmd = redis::cmd("SET");
        cmd.arg("x").arg(42);
        cmd.query_async(conn).and_then(|_| Ok(()))
    }).map_err(|_| ());

    let thread_pool = ThreadPool::new();
    thread_pool.spawn(work);
}

It does not compile due to:

the trait bound `futures::Future<Item=redis::async::Connection, Error=redis::RedisError>: std::marker::Send` is not satisfied
  --> src/main.rs:19:17
   |
19 |     thread_pool.spawn(work);
   |                 ^^^^^ `futures::Future<Item=redis::async::Connection, Error=redis::RedisError>` cannot be sent between threads safely
   |
   = help: the trait `std::marker::Send` is not implemented for `futures::Future<Item=redis::async::Connection, Error=redis::RedisError>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::ptr::Unique<futures::Future<Item=redis::async::Connection, Error=redis::RedisError>>`
   = note: required because it appears within the type `std::boxed::Box<futures::Future<Item=redis::async::Connection, Error=redis::RedisError>>`
   = note: required because it appears within the type `futures::future::chain::Chain<std::boxed::Box<futures::Future<Item=redis::async::Connection, Error=redis::RedisError>>, futures::AndThen<std::boxed::Box<futures::Future<Item=(redis::async::Connection, _), Error=redis::RedisError>>, std::result::Result<(), redis::RedisError>, [closure@src/main.rs:15:40: 15:50]>, [closure@src/main.rs:12:55: 16:6]>`
   = note: required because it appears within the type `futures::AndThen<std::boxed::Box<futures::Future<Item=redis::async::Connection, Error=redis::RedisError>>, futures::AndThen<std::boxed::Box<futures::Future<Item=(redis::async::Connection, _), Error=redis::RedisError>>, std::result::Result<(), redis::RedisError>, [closure@src/main.rs:15:40: 15:50]>, [closure@src/main.rs:12:55: 16:6]>`
   = note: required because it appears within the type `futures::MapErr<futures::AndThen<std::boxed::Box<futures::Future<Item=redis::async::Connection, Error=redis::RedisError>>, futures::AndThen<std::boxed::Box<futures::Future<Item=(redis::async::Connection, _), Error=redis::RedisError>>, std::result::Result<(), redis::RedisError>, [closure@src/main.rs:15:40: 15:50]>, [closure@src/main.rs:12:55: 16:6]>, [closure@src/main.rs:16:16: 16:22]>`

If I am not mistaken, this does not work, since RedisFuture is just a type alias to Box<Future<Item = T, Error = RedisError>> (note: there is no + Send in the box). If I add the annotation, then async::Connection::read_response does not compile. I did not follow the whole path, it looks like it boxes some types containing io::Read which is not Send-able.

I would love to look into this issue, but most likely I will need some support how to attack the problem. :)

[badboy]

cc @Marwes - I don't know about the details (and have yet to use the async code). Is there any chance we can make Redis' future RedisFuture Send?

[Marwes]

It seems like I only fixed this in #143. Probably not worth extracting it but it should just mean changing this line https://github.com/mitsuhiko/redis-rs/pull/143/files#diff-dfd26227c4842bd3288e9b1f53f0089fL352 .

Edit: Nvm, easier to just change it.

[boxdot]

@Marwes: Amazing. This is what I was missing. Needed to annotate T + other types as Send. Thanks!